Walls are typically framed with studs 16 inches on center, rafters and joists usually the same, but sometimes 24 inches on center. Ceilings are usually 8 feet high, or 10 feet in lots of newer construction.

6 Answers
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In Canada, while officially we are metric, all the construction work I've been around is done almost entirely in imperial. Everything comes in the same dimensions, and is referred to in feet and inches. Framing is done 16 or 24" on center, standard ceilings are 8' high.

Part of this may just be a hold-over from years of everyone doing that way, and then passing that on as they teach younger tradespeople. In school, I grew up learning the metric system, with the most exposure to feet/inches while doing fractions in math class.

I think part of it has to do with convenience and standardization as well: a "1.22 x 2.44m plywood" is awkward to say, and changing the dimensions slightly to 1.25 x 2.5 m would be strange. 16" (0.406m) centers is about the right distance for drywall, and so if you had 1.25m sheets of drywall, your centers would have to be 0.416m (or 16.4") to work out.. that's awkward to deal with.

Personally, I use a tape measure that has both centimeters and feet/inches on it, and often use cm if I'm measuring any more accurately than 1/8". One thing imperial has going for it, is the foot is a very handy size. There is no equivalent in metric (the decimeter (10cm / 0.1m / 3.9") is too small (plus no one ever says the word "decimeter"), while the meter (3.28ft) is too big).

The dimensions stay the same so you can do work on old houses. I just extended an 80 year old drywall (plasterboard) wall, the studs needed to be the same dimension as what was there before - no problem.
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Jeremy McGeeJul 24 '10 at 6:19

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@Jeremy: The problem with some old houses is that they used dimensional lumber. A 2x4 really was 2" by 4" rough cut so, in some cases, you have to use spacers to extend walls or do other similar work since a modern 2x4 has been milled to 1.5" by 3.5".
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Dennis WilliamsonJul 28 '10 at 20:40

The main reason why Canadian dimensions are still imperial is that something like 75% of the lumber manufactured here goes to the US.
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Chris CudmoreJun 11 '13 at 13:08

The following information is from Norway, but I would expect that the same dimensions are used elsewhere in Europe. The system used there parallels what we have here in the U.S., but the actual dimensions are different. Colloquially, terms like “two-by-four” are used, but the actual millimeter sizes are used in price lists, etc.

The dimensions referred to by the colloquial terms are quite a bit bigger than in the U.S. For instance, a U.S. milled four-by-four is actually 3.5 inches (89 mm). In contrast, a Norwegian milled “four-by-four” is actually 3.86 in (98 mm).

Studs, joists, and rafters are always spaced 60 cm (23.62 in) on center. The dimensions of OBS and other sheets are multiples of 60 cm in both dimensions so they can be placed in either direction, e.g., 60 x 240, 60 x 300, or 120 x 300 cm.

Depends on the country. Most English-speaking countries use imperial system, but convert all the dimensions into m/cm/mm and kg. For example, this is a 2x4

However, it's usually not an issue outside of US/Canada, as most of the other world doesn't build houses out of dimensional lumber. They use bricks, cement blocks, cement panels, etc. and the dimensions are almost always communicated in millimeters

(Un)fortuantely in Australia the dimensions are exactly the same. Which always throws me when I measure in MM and I go to the hardware store and they start talking in feet and inches.

It also answers questions about why some things are such incredibly odd dimensions. When you convert them from fractions-of-a-cm to feet/inches they usually fit some arcane measuring standard from the 1920s.

The Canadian building industry is almost entirely homogenized with the US building industry. We use the same products so we use the same labels. Everyone here knows that a 2x4 isn't really 2"x4". 1/2" copper pipe was supposed to be 1/2" ID but the walls were too thin so instead of expanding the OD and making the connectors not fit, they made the ID small, so neither dimension is 1/2".

There are a lot of similar examples. The exception is plywood and gyproc which are really the given dimensions and thicknesses. There are a couple of differences between Canada and the US: Canadian shingles are 1m long, whereas the US shingle is 3 ft. long. Other differences are usually in measuring small thicknesses such as plastic and glass; normal household glass is 3mm. Its a lot easier using millimetres than fractions of inches for small values.